//获取浏览器页面可见高度和宽度  
var _PageHeight = document.documentElement.clientHeight,  
    _PageWidth = document.documentElement.clientWidth;  
//计算loading框距离顶部和左部的距离（loading框的宽度为215px，高度为61px）  
var _LoadingTop = _PageHeight > 61 ? (_PageHeight - 61) / 2 : 0,  
    _LoadingLeft = _PageWidth > 215 ? (_PageWidth - 215) / 2 : 0;  
//在页面未加载完毕之前显示的loading Html自定义内容  
var _LoadingHtml = '<div id="loadingDiv" style="width: 100%;height: 100%; position: fixed;top: 0;left: 0;z-index:999"><img src="/DCVTools/img/loading.gif" style="width:250px;height:250px;position: absolute;top:50%;left:50%;margin-left: -110px;margin-top: -110px"></div>';  
//呈现loading效果  
document.write(_LoadingHtml);  
  
window.onload = function () {  
    var loadingMask = document.getElementById('loadingDiv');  
    loadingMask.parentNode.removeChild(loadingMask);  
};  
  
//监听加载状态改变  
document.onreadystatechange = completeLoading;  
  
//加载状态为complete时移除loading效果  
function completeLoading() {  
    if (document.readyState == "complete") {  
        var loadingMask = document.getElementById('loadingDiv');  
        loadingMask.parentNode.removeChild(loadingMask);  
    }  
}